The present invention relates to a method for determining the pedal force as a control quantity during braking with anti-lock control for a brake system with anti-lock control which includes as electromotively driven hydraulic pump. The electromotively driven hydraulic pump serves as a return of pressure fluid discharged from the wheel brakes during braking pressure control or for the generation of auxiliary pressure. The present invention also relates to a circuit configuration for implementing the method, and includes sensors for determining the wheel rotational behavior and an electronic controller for: (a) evaluating the sensor signals, (b) generating braking pressure control signals, and (c) actuating the electromotively driven hydraulic pump which serves for the return of pressure fluid or the generation of auxiliary pressure.
It is difficult to determine the pedal force and the resulting supply pressure in anti-lock brake systems. Of course, it would, in principle, be possible to determine the pedal force by way of force sensors, for example, by known wire strain gages. However, the complexity of such measuring apparatus would be great, in particular, because monitoring devices would be required in addition. As a result, such measuring apparatus is avoided for cost reasons, although the supply pressure takes major effect on braking pressure control. Therefore, it would be important for the control quantity and control comfort to have data about the supply pressure.
Japanese patent application JP-A-0 3096469 teaches monitoring the voltage variation directly after deactivation of the drive motor of a hydraulic pump, which pump is included in an anti-lock system, in order to detect defects or pressure fluid leakages. Either the steep or the gradual decline of the drive motor voltage is evaluated as a criterion.
Further, it is disclosed in DE-A-38 19 490 to monitor the electromotively driven hydraulic pump of an anti-lock brake system by means of sensors which determine and evaluate measured values indicative of the actual operating condition of the electric motor from time to time or continuously during operation of the hydraulic pump. This way, the operability of the hydraulics is monitored without direct measurement of the pressure.